Adjustable thermostatic switch



Dc. 4, 1934. I B. E. GETCHELL 1,983,077

ADJUSTABLE THERMOSTATIC SWITCH Filed Jan. 6, 1934 4 INVENTOR BENJAMIN E.GETCHELL 5thumb.piece;or.other adjusting device.

Patented Dec. 4, 1934 1,983,077 PATENT OFFICE ADJUS TABL E THERMOSTATICSWITCH Benjamin E. Getchell, Plainville, Conn., assignor toThe TrumbullElectric Manufacturing Company, Plainville, Conn.,

Connecticut a corporation of Application January 6, 1934, Serial No.705,491

7 Claims.

My invention relates particularly to a combination of electric heaterand switch provided with means of adjustment to vary the temperature atwhich the switch will operate.

One object is to provide a compact, enclosed type of thermostatic switchprovided with external means to permit adjustment.

Another object is to provide an enclosed snap action thermostatic switchwhich may be readily ;adjusted to operate at different temperatures.

Another object is to, provide a switch of the foregoing character inwhich the initial adjustments can be effected at the factory to remainfixed.

Another object-is to provide a heat actuated thermostatic switch whichcan be made economi cally and which is reliable in its operation.

Another object is to provide a simple compact type:.of heat actuatedswitch which can be readily ,;adjusted over a wide range oftemperatures.

.*Another object is to provide an adjustable thermostatic switch inwhichcan be readily embodied withoutchange of construction, an auxiliaryheateL-for the purpose of compensating for the differential oftemperature between the on and off? movements of the switch.

in .carrying .out the invention I preferably mount an. operatingmechanism inside of a casing which is sealed and is provided with anexternal The thermosta'tic' switch includes a bendable element whichsupportsthe bi-metallic strip in such a manner that both may be'adjustedto vary the action of theswitch.

If it is desirable to reduce the differential in temperature betweengthe,on and off movementsofg-the switch; the bendable element supportingthelei-metallic strip may be made of an electrical resistance material.

.Fig- 1 is a longitudinal sectional view of one form of device embodyingmy invention, showing the parts of the switch in the open circuitposition.

Fig. 2 isa side view of the switch mechanism removed from the casing.

Fig. 3 is a plan view of the same showing the parts of the switch in theclosed circuit position.

Fig.4 is a bottom view of the support for the 5(} switch with theadjusting mechanism.

6 action thiscontact 12 may be carried by an arm 14 hinged to the end ofthe strip 13 as set forth in application Ser. No. 701,714 filed December9, 1933 by Benjamin E. Getchell.

A washer 15 is supported by a knife edge like tip of the strip 13 and aspring 16 is interposed between the washer 15 and a shoulder on theswitch member so as to produce a toggle like action.

The arm 17 is preferably formed of bendable resistance metal and so asto serve as a support for one end of strip 13. Arm 17 may be formed ofresistance material to serve as a heater to compensate for differential.One end of this arm 17 is supported by a post-like member or members 18which are secured to the support 8. The other end of the arm 17 issecured to one end of the thermostatic strip 13 by rivets 19 withinsulating pieces 20, 20 on opposite sides. A back piece 21 may also beprovided to afford a seat for the adjusting screw 22 which passesthrough the strip 13 and the arm 1'7 so that by tightening or looseningthe screw 22 the relative position of the strip 13 with respect to thearm 17 may be adjusted.

The shaft 23 is supported in bearings 24 and has an eccentric pin 25 atits inner end located between the spaced apart ends of the insulatingpieces 20, 20. A finger piece 26 is provided on the outer end of theshaft 23 for rotating the shaft and thereby adjusting the heater arm 1'7and the thermostatic strip 13.

To hold the shaft 23 and associated parts in adjusted position I providea disc 27 on the shaft 23 which coacts with a spring finger 28 carriedby the support 9. The edge of the disc 27 is notched to provide definitepositions for the engagement of the spring finger 28.

p The finger piece 26 is preferably provided with an indicating pointeror mark 29 which is adapted to coact with the stationary scale 30 toshow the adjusted position of the parts.

A stationary stop 31 is provided opposite the post-like member 18 tolimit the movement of the thermostatic strip awayfrom the heater arm. Anabutment member 32 opposite the contact 10 limits the movement of theswitch member away from the contact 10.

The electrical parts are preferably housed in a casing made up of thetwo parts 33 and 34 which are suitably connected and one of which isprovided with an outlet 35 for the electric conductors. In order toprovide a water tight joint between the shaft 23 and the casing I mayprovide a soft rubber washer 36 and a metal washer 37.

When the parts are in the position shown in Fig. 3 electric currentpasses successively through the parts 11, 10, 12, 14, 13. 17 and 18.When the temperature changes so as to warp the thermostatic strip 13from the position shown in Fig. 3 toward the position shown in Fig. 1,the switch parts snap to the open circuit position, and vice versa, andwhen the temperature conditions change in the other direction, the partswill move from the positions shown in Fig. 1 to the positions shown inFig. 3.

' The temperatures at which these changes occur will depend upon theposition of the supporting arm 17. This position can be readily adjustedby simply rotating the finger piece 26 with the shaft 23 and the crankpin 25. The scale 30 may be calibrated to indicate temperature'points atwhich the changes take place, such calibration being in accordance Wtihany suitable code or thermometric standard. The primary adjustment forraising or lowering the adjustable range is efiected by means of thescrew 22 which adjustment, of course becomes fixed for a giveninstrument if the parts are sealed in the casing.

When this supporting arm 17 is also used as a heater, it is not for thepurpose of moving the bi-metallic strip to produce action of thecontacts. t is for the purpose .of moving the strip just enough tocompensate for the difierential between the normalopening and closingtemperatures of the thermostat so that a slight further change inexternal temperature will cause switch action.

-compensation-with a setting of 60 degrees, the

' thermostat would snap on at 60 degrees and off at '72 degrees, adiiferential of 12 degrees.

When the thermostat is controlling a fixed load, it is possible to makearm 17 of resistance metal of just the right resistance to add apre-determined amount of heat to the thermostat, independent of outsidetemperature. For instance, if this resistance added 11 degrees of heatto the thermostat, an outside temperature increase of 1 degree would besufiicient to cause it to trip Thus the differential would be reduced to1 degree instead of 12 degrees, making it possible to more closelyregulate the heating of hotbeds, etc.

This construction has the added advantage over the ordinary enclosedthermostatic switch in that it can be actuated manually to open andclose the circuit independently of changes in temperature. For instance,if the parts are normally in the open circuit position of Fig. 1, theswitch can be manually actuated to the position of Fig. 3 by simplyturning the finger piece 26 and without waiting for the temperaturechange;

I claim:

l. A thermostatic switch including a bendable arm supported at one endand free at the'-other end, a bi-metallic strip having one end securedto and movable with the free end of said arm, a

switch contact carried by the opposite end of said i 1 strip, means foradjusting the position of the strip with respect to the arm to vary theaction of the strip with respect to, the arm, and means for adjustingthe free end of said arm and the attached end of said strip to vary themoment of action of the switch.

2. In a thermostatic switch a heater element, a bi-metallic stripsupported thereby, 39%!!5 Or relative thereto.

adjusting said strip with respect to said heater element, and means foradjusting one part of said heater element with said strip.

3. In a thermostatic switch, a stationary contact, a bi-metallic stripmovable across a predetermined point under the influence of changes intemperature, a contact member carried by said strip and being adapted tomove into engagement with the stationary contact under snap action uponthe movement of the strip across said point, a heater arm for heatingsaid strip and manual means for variably adjusting the position of saidarm and strip relative to said point, said means including a crank shaftoperatively connected to 'said arm and strip and a finger piece for actuating said shaft. j

4. In a thermostatic switch, a stationary contact, abi-metallic stripmovable across a predetermined point under the influence of change oftemperature, a contact member carried by said strip .and being. adaptedto move .into engagement with the stationary contact under snap actionupon the movement of the strip across said point, a heater arm forheatingsaid strip and manual means for initially adjusting the positionof said arm and strip relative to said point, and means to indicate thepositions of said arm and strip relative to said point, said meansincluding a crank shaft, a dial and a pointer carried by-the crankshaft.

5. In a thermostatic switch, a stationary contact, a bi-metallic stripmovable across a predetermined point under the influence of heat, acontact member carried by said strip and being adapted to move intoengagement with the sta-' tionary contact under snap action upon themovement of the strip across, said point, a heater arm for heating saidstrip, manual means for initially adjusting the position of said arm andstrip relative to. said point, said means including a crank shaft havinga member engaging the heater arm to move the same and means for holdingthe crank shaft in adjusted positions.

6. In a thermostatic switch, a stationary contact, a bi-metallic stripmovable across a predetermined point under the influence of changes intemperature, a contact member carried by said strip and being adapted tomove into or out of engagement with the stationary contact under snapaction upon the movement of the strip across said point, a heater armfor heating said strip, means for initially adjusting the position 'ofsaidstrip relative to said arm', means for variably adjusting theposition of said arm and strip relative to said point, said latter meansincluding a crank shaft havinga portion connected to the heater arm anda manually operable member for rotating the crank shaft and means toindicate the said predetermined point and the adjusted position of thearms and strip '7. A thermostatic switch including a casing, aninsulating support therein, a stationary contact on said support, abi-metallic strip movable across a predetermined point on said support,a contact member carried by said strip and being adapted to move into orout of engagement with the stationary contact under snap action upon themovement of the strip across said point, a heater arm for heating saidstrip and means positioned exteriorally of the casing for readilyadjusting the position of the arm and strip relative to said point.

BENJAMIN E. GETCHELL.

